Apparatus for rotation of tailgate assembly

ABSTRACT

In a tailgate assembly, a connecting mechanism which joins one end of each side plate of the assembly to the frame of the vehicle carrying the assembly wherein pivoting of the dump body of the vehicle causes the connecting mechanism to rotate the tailgate assembly. The connecting mechanism includes a chain on each side of the body which is biased about the side of the body by a roller assembly that engages the chain to hold it away from the side and to limit its lateral movement along the length of the side.

TECHNICAL FIELD

The invention generally relates to tailgate assemblies for off-road,heavy-duty trucks and more particularly relates to mechanisms forraising and lowering tailgates.

BACKGROUND

Because tailgate assemblies can be damaged by the difficult tasksperformed by the off-road, heavy-duty trucks, the bodies of the truckshave traditionally been designed to function without tailgates. But, asa result of a desire to increase capacity, tailgate assemblies have beendesigned for addition of tailgates to the bodies which are capable ofwithstanding the harsh working environment of off-road trucks. Forexample, in U.S. Pat. No. 3,751,112 to Hagenbuch a tailgate assemblyincludes two side plates that are pivotally connected to the sides ofthe body. In order to raise the tailgate upon the pivoting of the body,a pair of outriggers mounted to the frame of the truck, secure one endof a pair of chains (or cables) which cause the tailgate to rotate whenthe body is dumped.

By providing outriggers, the chains or cables which rotate the tailgateare attached at a point on the frame which extends out beyond the sideof the body. By attaching one end of the chains at the end of theoutriggers, the chains are not biased around the bottom edge of thebody, which would cause damage to both the chains and the truck body.

But, because the outriggers are a cantilever and extend from the frameto a point beyond the sides of the body, the outriggers may be plaguedwith problems under certain conditions. For instance, because of limitedavailable space on the frames of some truck models, the area of the baseof the outriggers (where they attach to the frame) may be smaller thandesired. The strength of the outriggers may be compromised if the basesof the outriggers have areas too small for the outriggers to withstandthe large forces exerted at the ends of the outriggers as the tailgateis rotated when the body pivots. As a result of the area of the basebeing too small, the outriggers may be susceptible to bending afterrepeated use. Finally, some manufacturers of trucks are reluctant tohonor warranties if the frame of the truck has been subjected to weldingas is required to mount the outriggers for the addition of a tailgateassembly.

One attempt at eliminating the potential problems of the use ofoutriggers to raise tailgates has been to use a shortened outriggerwhich does not extend beyond the sides of the body. By shortening theoutrigger, the weakening caused by cantilevering is reduced. Becausethese outriggers do not extend beyond the sides of the body, the chains(or cables) are biased against the bottom edge of the body. When thebody is pivoted to a dump position, the chains move relative to thebottom edge of the body. In order to prevent damage of the body or thechains as the body pivots in dumping, an elongated roller is mounted oneach side of the body in order to protect the truck body and reduce wearof the chain.

Each roller is elongated because, as the body pivots, the chain changesposition along the length of the sides of the body. As a result, inaddition to the roller rotating as the chain pulls the tailgate to araised position, the chain also walks along the length of the roller asthe relative positions of the chain and roller change. Because offrictional forces, the chain does not walk smoothly along the length ofthe roller; instead, it moves in a jerking motion caused by the frictionbetween the roller and chain holding it in a stationary lateral positionuntil movement of the body and tailgate cause an angle in the chainwhich creates sufficient force to overcome the friction. As the bodycontinues to pivot, the forces created by the bending chain increaseuntil they again overcome the friction and the chain snaps to a newposition. This jerking movement is extremely hard on both the rollers,the chains, the outrigger, the tailgate and the truck frame. As aresult, the rollers and chains wear out quickly.

To overcome the foregoing wear problem, it is known to use a cableconnection instead of a chain. Because a cable is composed of multiplestrands of wire, frictional forces between strands become substantial ifthe elongated rollers bend the cable at too great an angle. In order toreduce the angle, the shortened outriggers are provided. Although theamount of extension of these shortened outriggers reduces problemsinherent in a cantilevered support off the truck frame, the problemsremain.

SUMMARY OF THE INVENTION

The primary objection of the invention is to provide a mechanism forraising and lowering a tailgate assembly which does not have theforegoing disadvantages associated with both full truck width andshortened outriggers. In this connection, it is also an object of theinvention to provide a mechanism for raising and lowering tailgateassemblies that fulfills the foregoing objective without introducing newdisadvantages as exemplified by the foregoing prior attempts.

It is another object of the invention to provide a tailgate assemblywhich can be easily added to existing truck bodies without compromisingthe structural integrity of the frame or body.

Other objects and advantages will become apparent with reference to thefollowing detailed description when taken in conjunction with thedrawings.

The invention provides an improved connecting mechanism joining thetailgate assembly of a dump body and the frame of the vehicle whichfunction to rotate the tailgate assembly in response to pivoting of thedump body. In order to join the connecting mechanism to both thetailgate assembly and the frame, it is angled about the side sheets ofthe body. The connecting mechanism is biased away from the side sheetsby a pair of roller assemblies mounted to the bottom sheet of the bodyof the tailgate assembly. In order to prevent repositioning of theconnecting mechanism along the length of the side sheets as the bodypivots and the tailgate rotates, the roller assembly includes means forlimiting the lateral movement of the mechanism. The means resistslateral movement of the connecting mechanism, thereby biasing themechanism in a plane parallel to the side plates.

While the invention will be described in some detail with reference to apreferred embodiment, it is to be understood that it is not intended tolimit the invention to such detail. On the contrary, it is intended tocover all alternatives, modifications and equivalents which fall withinthe spirit and scope of the invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heavy-duty, off-road truck with thebody of the truck in its fully pivoted position in order to most clearlyshow the connecting mechanism for raising and lowering the tailgateassembly of the body according to the invention;

FIG. 2 is a side view of the truck showing the body in its fully loweredposition in order to illustrate the position of a chain in a rollerassembly of the connecting mechanism;

FIG. 3 is a rear view of the truck showing the body in its fully loweredposition, taken along the line 3--3 in FIG. 2;

FIG. 4 is a side view of the body of the truck in a full pivotedposition illustrating the position of the chain of the connectingmechanism of the invention relative to its position when the body isfully lowered as shown in FIGS. 2 and 3;

FIG. 5 is a front view of the fully pivoted body taken along the line5--5 in FIG. 4; and

FIG. 6 is an enlarged perspective view of one of the two rollerassemblies of the connecting mechanism according to the invention with aportion of the assembly cut away to more clearly illustrate the relativepositions of the pair of rollers in the assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown the typical rear dump vehicleillustrated in the dump position. The rear dump vehicle includes a dumpbody 11 having a pair of side sheets 13 (one sheet shown only), a frontsheet 15 and a bottom sheet 17. Furthermore, some rear dump vehiclesinclude a canopy 19 coupled to the dump body 11. The canopy operates toprotect a cab 21 when the rear dump vehicle is being loaded. The sidesheets 13, the front sheet 15 and the bottom sheet 17 provide an opentop wherein earth or other loaded material can be inserted in the dumpbody 11. The dump body 11 is generally connected to the main frame 23 bya body pivot assembly 25 so that the body can be rotated about a bodypivot pin 25a for dumping the load.

A tailgate assembly 27 is illustrated having a pair of side plates 29(one of which is illustrated only) and a rear plate 31. The side plates29 are pivotally connected to the side sheets 13 of the dump body 11 bya tailgate pivot pin 33. Consequently, the tailgate 27 can pivot aboutthe pivot pin 33 to provide both a dump position (as shown in FIG. 1)and a load position (as shown in FIG. 2). The rear plate 31 of thetailgate 27 is illustrated in FIG. 2 as extending beyond the rearportions of the side sheets 13. Furthermore, the rear plate 31 is shownsubstantially perpendicular to a ground surface. Consequently, the rearplate 31 when in the load position provides an increased volume for thedump body 11 in which loaded material can be placed.

The forward edge of the side plates 29 of the tailgate assembly 27 haveextension pieces 35 thereon which provide an anchor for a chain 37. Atthe opposite end of the chain 37, it is connected to an elongatedmounting support 39. The mounting support 39 is in turn welded to a basesection 40 for the hoist cylinders 42. As an aid in describing relativemovement of the dump body 11, the tailgate assembly 27 and the chain 37,a Cartesian coordinate system is illustrated with a Y-axis alignedparallel with the axis of rotation for the dump body and the X-axisparallel with the length of the vehicle. The Z-axis is substantiallyvertical.

As the forward portion of the dump body 11 is raised by the hoistcylinders 42, the dump body is pivoted about the body pivot pin 25a.Pivoting of the dump body 11 causes the chain 37 to become taut and, asa result, exerts a torque on the side plate 29 which causescounterclockwise rotation of the tailgate assembly 27 about the pivotpin 33. As illustrated in FIG. 1, pivoting of the dump body 11 causesthe rear plate 31 to rotate to a position which substantially clears thenormal maximum load height of loaded material carried in the dump body.Consequently, any material on the bottom sheet 17 of the dump body 11can be discharged beneath the rear plate 31 of the tailgate assembly 27and through the rear portion of the side sheets 13.

The tailgate pivot pin 33 can be located at any desired positionrelative to the side plate 29 of the tailgate assembly 27 and the sidesheets 13 of the dump body 11. However, a desired position for thetailgate pivot pin 33 is in a position which causes a slight raising ofthe rear plate 31 of the tailgate assembly 27 to an angle approximately90° between the top of side sheets 13 and the top of side plate 29. Aslight raising of the rear plate 31 provides increased clearance betweenthe rear plate and the bottom sheet 17 for discharge of the loadedmaterial. By placing the pivot pin 33 substantially forward from therear of the side sheets 13 (as shown in FIG. 1), rotating motion of thesurface of the rear plate 31 is upwardly and over the loaded material.

The mounting support 39 is preferably an elongated, square and hollowtubing (e.g., steel) which is secured to the lowermost portion of thebase section 40 which anchors one end of each of the hoist cylinders 42.Although the mounting support 39 eliminates the need for outriggers, thechain 37 can no longer maintain a straight line in the Y-Z plane, as itcould when an outrigger was present.

As best seen in FIG. 3, a straight line SL in the Y-Z plane connectingthe extension piece 35 to the end 39a of the mounting support 39 cutsthrough the side walls 13 and the bottom 17. Therefore, the chain 37must be biased around the edge 41 formed where the side 13 meets thebottom 17. In order to direct the chains 37 around their respectiveedges 41, a pair of roller assemblies 43 are mounted (e.g., welded) onthe bottom sheet 17 and adjacent the edges 41 in order to engage thechains 37 and prevent scraping of the edges against the chains as theymove relative to one another as the dump body 11 pivots.

Referring more particularly to FIGS. 2 and 3, in the lowered position ofthe dump body 11, each of the chains 37 describe a straight line in theX-Z plane and an angled line in the Y-Z plane. The angling of the chain37 in the Y-Z plane is provided by a cylindrical roller 45 in each ofthe roller assemblies 43 which causes the chain to be biased away fromthe edge 41. Because the roller 45 is mounted for rotation about an axisr₁ which is substantially transverse to the line formed by the chain 37in the X-Z plane, pivoting of the dump body 11 will cause the roller 45to rotate as the chain moves over the surface of the roller.

In accordance with one important aspect of the invention, each of theroller assemblies include a second roller whose axis of rotation isapproximately transverse to that of roller 45; when the chain is biasedaway from the edge 41 in the Y-Z plane by the roller 45 during pivotingof the dump body 11 and rotation of the tailgate assembly 27, the chainalso is biased forwardly in the X-Z plane by the second roller so thatthe sliding of the chain along the length of the roller 45 is limited.Each of the second rollers is mounted in the roller assembly relative tothe first roller 45 so as to engage the chain 37 as it begins to movelaterally along the length of the surface of roller 45 in response tothe pivoting of the dump body 11 and the rotation of the tailgateassembly 27. After the second roller engages the chain 37, furtherpivoting of the dump body 11 will cause the chain 37 to angle about thesecond roller in the X-Z plane. Because the chain 37 is biasedforwardly, the first roller 45 is able to hold the chain away from theedge 41 without being of a substantially longer length. In addition, bylimiting the amount of travel of the chain 37 along the length of theroller 45, the wear caused by such lateral movement is substantiallyreduced. Because the chain no longer catches and releases in response tothe frictional dynamics of the chain moving laterally over an elongatedroller as in the prior art, the raising and lowering of the tailgateassembly 27 in accordance with the invention is much smoother thanpreviously possible in tailgate assemblies without outriggers.

Viewing the dump body 11 from the side and in its lowered position asillustrated in FIG. 2, the chain 37 appears as aligned substantially ina straight line. Actually, the chain 37 is angled in the Y-Z plane aboutthe edge 41 by the first roller 45, as best seen in FIG. 3, whose axisof rotation r₁ is in approximate parallel alignment with the edge 41.When the operator of the vehicle activates the hoist cylinders 42, thedump body 11 pivots, thereby causing the roller assembly 43 and thetailgate assembly 27 to rotate about the pivot pin 25a. As the dump body11 pivots toward its dump position shown in FIGS. 4 and 5, the extensionpiece 35 moves relative to the roller assembly 43 and the mountingsupport 39.

Since the chain 37 remains taut as the dump body 11 pivots, it attemptsto maintain a straight line between the extension piece 35 and themounting support 39. In attempting to maintain such a straight line, thechain moves along the length of roller 45 as the relative positions ofthe extension piece 35 and mounting support 39 change. Because roller 47is mounted for rotation about an axis r₂ that is transverse to the axisof rotation r₁ for roller 45, when the chain 37 reaches the surface ofthe roller 47 it is prevented from traveling further along the length ofroller 45, and it is biased by the surface of the roller so thatcontinued pivoting of the dump body 11 causes the chain 37 to rotate theroller as the chain becomes angled in the X-Z plane as well as the Y-Zplane.

Referring to FIG. 6, each of the roller assemblies 43 includes first andsecond metal plates 49 and 50 which are mounted on the edges to thebottom sheet 17 of the truck body 11. At the free ends of the plates 49and 50, metal cross members 51 and 53 brace the plates so as to providea sturdy open box structure. Spanning plates 49 and 50, the journals ofroller 45 are received by holes in the plates which are surrounded bybushings 62 (only one is shown) mounted on the outside surface of eachof the plates. Likewise, roller 47 spans the opposing cross members 51and 53 with its journals being received by holes in each of the crossmembers which are surrounded by bushings 60 mounted on the outsidesurface of the members. To further support the roller assembly 43,struts 65 (only one is shown in FIG. 2) extend from the outside of theplates 49 and 50 to the surface of the bottom sheet 17.

Each of the rollers 45 and 47 is constructed of large and small tubingconcentrically positioned and capped at both ends by a donut-shapedmetal piece. The foregoing construction creates a central bore througheach roller 45,47 that receives an elongated rod that serves as a shaftabout which the rollers rotate. The ends of the shafts serve as thejournals which are received by the bushings 62 and 60. As a possibleaddition to the roller assembly, a layer of rubber may be vulcanized toits circumference in order to further improve the smoothness of themovement of the chain 37 over the surface of the roller.

The extension piece 35, roller assembly 43 and mounting support 39 maybe moved relatively to one another from their positions shown in thedrawings in order to provide for varying degrees of tailgate rotationwhich maximizes the opening of the tailgate relative to the body.Because such repositioning may result in the chain 37 rubbing the plate50 of the roller assembly 43, a third roller mounted in the assembly mayprove necessary. By simply extending the length of the cross members 51and 53 and the length of the roller 45, the third roller can be addedwhich is supported by the cross members on the forward side of the chain37. The third roller may have an axis of rotation parallel with the axisof rotation r₂ of the second roller 47.

In keeping with the invention, the chain 37 may be a single continuouschain which reaches from one extension piece 35 to the other as bestshown in FIGS. 3 and 5. For a continuous chain 37, the mounting 39 ispreferably a conduit through which the chain passes. A single continuouschain 37 responds to changes in the tension of the chain on each side ofthe body resulting from uneven tilting of the body. If this happens, thedistance between the ends 39 of the mounting support 39 and theextension pieces 35 will increase on one side and decrease on the otherside. By making the chain 37 continuous, any shifting or tilting of thebody 11 is compensated for by movement of the chain through the hollowof the support mounting 39.

If the chain 37 breaks, release of the chain's tension on both sides ofthe body can be avoided by limiting the chain's freedom of movementthrough the mounting support 39. For example, a short auxiliary chainmay attach the chain 39 to the mounting support such that a break on oneside will permit only a limited release of the tension on the opposingside because the auxiliary chain will hold the unbroken side to themounting support.

The preferred way of implementing the chains 37 is to provide twoseparate chains whose ends are secured to the ends 39a of the mountingsupport 39 thus tending to stabilize the tilting of the body. In orderto attach the ends of each separate chain 37 to the ends 39a of themounting support, the ends 39a are formed by welding a metal plate (notshown) over each end of the mounting support 39. Two support brackets(not shown) are positioned to be standing on end with the metal plate astheir base. These support brackets receive a nut and bolt assembly thatalso receives the last link of the chain 39. Because the last link issandwiched between the two support brackets, the nut and bolt assemblysecures the end of the chain 37 to the mounting support 39.

From the foregoing, it will be appreciated that the connecting mechanismof the invention provides an effective means for raising and lowering atailgate assembly for heavy-duty, off-road trucks without necessitatingthe use of an outrigger. Furthermore, the dual-roller assembly 43 allowsthe chain 37 to easily move relative to the dump body 11 without jumpingand without requiring cumbersome accessory equipment in lieu ofoutriggers.

I claim:
 1. In a rear dump vehicle of the type having a main frame and apair of side sheets, a bottom sheet and a forward sheet that form a dumpbody, an improved tailgate assembly compriising:a pair of side platespivotally connected to the side sheets of the dump body, each of thepair of side plates having first and second ends and a pivot pointintermediate said first and second ends; a rear plate coupled betweenthe second ends of each of the pair of side plates for providing a rearwall of said dump body; anchor means connected to the main frame of therear dump vehicle, and being located on the main frame under the bottomsheet of the dump body so as to not extend substantially beyond the sidesheets of said dump body; linkage means coupled between the first end ofeach one of said pair of side plates and said anchor means for providingrotation of said rear plate in response to counter rotation of the dumpbody, said linkage means spanning lower side edges of said dump bodyformed at the junction joining said pair of side sheets and said bottomsheet; a pair of roller assemblies, each mounted on the bottom sheet ofsaid dump body adjacent the side edges for (1) biasing said linkagemeans away from said lower side edges, (2) preventing friction betweensaid linkage means and said pair of side sheets during pivoting of thedump body and (3) inhibiting displacement of the linkage means along thelength of said pair of side sheets; each of said roller assembliescomprises a first cylindrical roller mounted in said assembly forrotation about a first axis substantially parallel with said pair ofside sheets, said first roller biasing said linkage means away from oneof said pair of side sheets; and a second cylindrical roller mounted insaid assembly for rotation about a second axis which is substantiallytransverse to said first axis, said second cylindrical roller biasingsaid linkage means so as to limit its lateral movement along the lengthof said first cylindircal roller during the pivoting of said dump bodyand the rotation of said tailgate assembly.
 2. An improved tailgateassembly as set forth in claim 1 wherein said linkage means includes atleast one chain which is angled between its connected ends by one ofsaid roller assemblies.
 3. An improved tailgage assembly as set forth inclaim 2 wherein said linkage means includes a single length of chainhaving an attachement means at each end of the chain for connecting toone of said pair of side plates; and said anchor is a conduit whichreceives said chain and allows free movement of the chain through theconduit such that the tension in each portion of said single lengthchain spanning one of said side plates and said anchor is approximatelyequal.
 4. A mechanism for rotating a tailgate assembly mounted forrotation on a dump body of a vehicle in response to pivoting of the bodyabout the frame of the vehicle wherein said dump body includes a bottomsheet, two opposing side sheets and a front sheet with said side sheetsmeeting said bottom sheet at a junction defining side edges of saidbody, said mechanism comprising:a pair of roller assemblies, eachmounted on the bottom sheet of said dump body adjacent the side edge;linkage means joining said tailgate assembly to said frame whereby saidlinkage means is biased away from said side edges by said rollerassemblies in a manner so as to create angles in said linkage means thatlie approximately in a first plane that is substantially transverse to asecond plane which is substantially parallel with said side sheets;means for pivoting said dump body on said frame; said linkage meansresponding to the pivoting of said dump body to generate a torque onsaid tailgate assembly, thereby causing rotation of said tailgateassembly about said side sheets; and each of said roller assembliesincluding means (1) for angling said linkage means in said second planein addition to said first plane as said body pivots and said tailgateassembly rotates so that said linkage means is biased along the lengthof said side edge by said means (1) to limit repositioning of thelinkage means along the length of the side edge as the body pivots andthe tailgate assembly rotates.
 5. A mechanism as set forth in claim 4wherein each of said roller assemblies comprises:a first cylindricalroller mounted in said assembly for rotation about a first axissubstantially parallel with said side edge, said first roller biasingsaid linkage means so as to be angled in said first plane; and saidmeans (1) comprising a second cylindrical roller mounted in saidassembly for rotation about a second axis substantially transverse tosaid first axis, said second roller biasing said linkage means so as tobe angled in said second plane.
 6. A mechanism as set forth in claim 5wherein said linkage means comprises at least one length of chain whichmoves over the surfaces of said first and second rollers as the dumpbody pivots and the tailgate assembly rotates.
 7. In a hauling vehicle,a tailgate assembly mounted to dump body having two opposing side sheetsjoined to a bottom sheet to form side edges and chain means extending oneach side of the vehicle joining the tailgate assmsbly and the frame ofthe vehicle for rotating the tailgate assembly in response to pivotingof the body, a pair of roller assemblies for angling said chain meansaround the side edges of said dump body, each roller assemblycomprising:a housing for mounting to the bottom sheet of said dump bodyat an area adjacent said side edge; a first cylindrical roller mountedin said housing for rotation about a first axis such that when saidhousing is mounted on said bottom sheet said chain means is biased awayfrom said side sheet by said first cylindrical roller so as to anglesaid chain means around said side edge in a plane substantiallytransverse to a plane coincident eith said side sheet; a second rollermounted in said housing for rotation about a second axis which issubstantially transverse to said first axis such that when said housingis mounted on said bottom sheet said chain means is biased for limitedmovement along the length of the first roller as the dump body pivotsand the tailgate assembly rotates so as to angle said chain means in aplane substantially parallel to said plane coincident with said sidesheet.
 8. A roller assembly as set forth in claim 7 wherein said housingincludes:first and second opposing plates wherein a portion of whoseedges are intended for mating with the bottom sheet of said dump body;first and second cross members joining said first and second opposingplates; and said first and second cylindrical rollers being mounted forrotation in said housing such that one roller spans said first andsecond opposing plates and the other roller spans said first and secondcross members.